The present application is based on and claims priority from Japanese Patent Application 2000-81406 filed Mar. 23, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a plane commutator that has a disk-like commutator surface and a method of manufacturing such a commutator.
2. Description of the Related Art
A plane commutator that has a disk-like flat commutator surface is installed in a motor such as a motor of a motor-integrated fuel-pump unit. The plane commutator is fitted to a rotary shaft of the motor. The plane commutator is comprised of a plurality of commutator segments (generally made of a burnt carbon) insulated by slits from each other, a plurality of metal base plates, and a resinous boss member. The plurality of the commutator surface forms the flat commutator surface. Each of the commutator segments is connected to one of the metal base plates.
There are two types of the plane commutator: the first type has the metal base plate connected to an end of the commutator and the commutator surface formed at the other end of the commutator; and the second type has the metal base plate connected to portions around the same end of the commutator as the commutator surface.
In the first type, it is difficult to mechanically fix the base plates to the commutator due to spring-back force of the base plate. Therefore it is necessary to weld or solder the base plates to the commutator segments while pressing the base plate in the axial direction thereof.
U.S. Pat. No. 5,925,961 or its corresponding Japanese Application, JP-A-10-4653, discloses a method of fixing the base plate to commutator segments of the first type commutator. Each commutator segment has a projection extending in the axial direction from the surface of the commutator opposite the commutator surface. The metal base plate has holes to which the projections are inserted. The holes are thereafter crimped or pressed at the circumference thereof to mechanically fix the base plate to the commutator segments.
However, it is difficult to control the pressing force to provide a desired strength in the disclosed method. If the pressing force is not controlled as desired, the projection may be broken. This is an obstacle to mass-production of the above type of the motors.
A main object of the invention is to provide an improved motor and a method of manufacturing such a motor.
In a plane commutator according to a preferred embodiment of the invention, a disk-like commutator surface is formed of a plurality of commutator segments at an end thereof and a base portion is formed at the other end, and each commutator segment has a tapering projection. A plurality of metal base plates is respectively connected to the plurality of commutator segments at the base portion. Each base plate has an expansible through hole force-fitted to the tapering projection, and each projection includes metal powder at portion in contact with the through hole.
Therefore, it is easy to control the elastic binding force without using any specific tool, and the projection can be prevented from being broken or damaged.
Preferably, each metal base plate has a tapering sleeve extending from the through hole to be in contact with the projection. The sleeve may have a plurality of slits for providing more suitable elastic contact with the projection.